Mould for forming the headpiece of deformable tubular plastic containers

ABSTRACT

The mould comprises a punch ( 10 ) having an outer surface ( 11 ′) arranged to engage the container tubular body ( 51 ) as an exact fit, and an end portion ( 13 ) projecting axially from the lower end of the cylindrical outer surface ( 11  ′), and a die ( 30 ) arranged to form, in combination with the lower surface ( 13 ′) of the punch, a cavity (F) for forming the headpiece ( 52 ) of the container; the die ( 30 ) has a concave surface ( 32 ′) arranged to receive as an exact fit, by axial penetration, the lower end of the cylindrical outer surface ( 11 ′) of the punch together with the lower end of the tubular body ( 51 ) of the container. The headpiece ( 52 ) is formed within the forming cavity (F). According to the invention, the punch ( 10 ′) comprises a radial deformation means ( 22, 25, 62, 65 ), positioned on its outer surface ( 11 ′) and extending annularly along the entire circumference of this surface to act on the tubular body ( 51 ) of the container, and is arranged to assume a normal position in which its outer surface does not project radially from the cylindrical outer surface ( 11 ′) of the punch, and an active position in which it is urged in a centrifugal direction in such a manner as to press the tubular body ( 51 ) against the opposing surface of the die, means being provided to urge the radial deformation means ( 22, 25, 62, 65 ) in the centrifugal direction during the forming of the container headpiece ( 52 ).

TECHNICAL FIELD

This invention relates to the forming of the top portion of deformabletubular plastic containers formed from a tubular body and a plasticheadpiece bonded to one end of the tubular body.

BACKGROUND ART

For this purpose, moulds are known comprising a punch having a lower endportion which penetrates into the cavity of a lowerly positioned die todefine, in combination with this latter, a cavity for forming thecontainer headpiece; the punch possesses a cylindrical outer surfacearranged to exactly engage the tubular body of the container, the lowerend of which is positioned adjacent to the edge of the forming cavityand penetrates through the cylindrical surface of the die as an exactfit, to couple the punch to the die.

The container headpiece is formed within the forming cavity and ishot-bonded under pressure to the lower end of the tubular body,typically by making the punch and die approach each other axially afterinserting a plastic blank into the forming cavity; alternatively, thiscan be done by injecting fluidized plastic into the forming cavity whilein the static configuration.

In this manner a tubular container is produced composed of the tubularbody and the headpiece, which usually possesses a threaded mouth throughwhich the container contents are extracted.

The mouth of the forming cavity is closed by the lower end portion ofthe cylindrical surface of the punch, which penetrates axially as anexact fit, together with the lower end of the tubular body, within thecylindrical concave surface of the die. As the pressure in the formingcavity is very high during the forming process, said mutually engagingcylindrical surfaces of the punch and die (with the tubular bodyinterposed) must mate with very little gap therebetween, in particularto prevent upward seepage of the plastic material, which would result inundesirable filament-like protuberances projecting into the containerchamber.

Because of this, the insertion of the punch into the die during themutual axial approach stage is a delicate and critical operation whichconsequently requires a relatively lengthy time and particular care;moreover the risk of said undesirable filament-like protuberancesforming cannot be eliminated in practice.

The applicant is aware of a mould for forming the top of deformabletubular plastic containers comprising a tubular body and a headpiece ofplastic material bonded to one end of the tubular body.

The mould comprises a punch having an outer surface arranged to engagethe container tubular body as an exact fit, and an end portionprojecting axially from the lower end of the cylindrical outer surface).

A die is arranged to form, in combination with the lower surface of thepunch, a cavity (F) for forming the headpiece of the container.

Said die has a concave surface arranged to receive as an exact fit, byaxial penetration, the lower end of the cylindrical outer surface of thepunch together with the lower end of the tubular body of the container.

The headpiece is formed within the forming cavity (F) and ispressure-bonded therein to the lower end of the tubular body by a radialdeformation means of the punch, positioned on its outer surface andextending annularly along the entire circumference of this surface toact on the tubular body of the container, said means being arranged toassume a normal position in which its outer surface does not projectradially from the cylindrical outer surface of the punch, and an activeposition in which it is urged in a radial direction in such a manner asto press the tubular body (51) against the opposing surface of the die.

The above features are partially disclosed by EP-A-0810073, but are notsuitable to overcome the above said drawbacks.

An object of this invention is to provide a mould able to overcome saiddrawbacks.

DISCLOSURE OF THE INVENTION

This and further objects are attained by the invention as characterisedin the claims.

The invention is based on the fact that the punch comprises a radialdeformation means, positioned on its cylindrical outer surface, whichextends annularly along the entire circumference of this cylindricalouter surface and acts on the inner surface of the container tubularbody in correspondence with the cylindrical concave surface of the die;this means is arranged to assume a normal position in which its outersurface does not project radially from the cylindrical outer surface ofthe punch, and an active position in which it is urged in a centrifugaldirection in such as manner as to press the tubular body against thecylindrical concave surface of the die, means being provided to urge theradial deformation means in a centrifugal direction during the formingof the container headpiece.

The radial deformation means is maintained in its normal position whilethe tubular body of the container is being fitted over the punch inorder not to hinder the penetration of the punch; it is also maintainedin its normal position when the punch together with the tubular body isinserted axially within the cylindrical concave surface of the die,again in this case not to hinder penetration.

Subsequently, during forming, it is thrust in the centrifugal directionin order to press the container tubular body against the cylindricalconcave surface of the die, along the entire circumference of the outercylindrical surface of the punch.

In this manner an outer sealed region is created which hermetically andeffectively seals the forming cavity, whatever the gap existing betweenthe mutually engaging cylindrical surfaces within that region.

According to a different embodiment, said radial deformation means isprovided within the die, on the concave surface thereof, and operates bypressing the tubular body against the opposing surface of the punch.

Proper success of the forming operation is therefore assured, even ifrelatively large gaps are present between the punch and die, with thepractical result that the formation stage of the container headpiece isfaster, more reliable and problem-free.

The invention is described in detail hereinafter with the aid of theaccompanying figures, which illustrate one embodiment thereof by way ofnon-exclusive example.

FIG. 1 is an axial section through that mould part incorporating a firstembodiment of the invention.

FIG. 2 is an enlarged detail of FIG. 1.

FIGS. 3A, 3B, 3C and 3D show that mould part of FIG. 1 in foursuccessive working stages.

FIGS. 4A and 4B show an enlarged detail of that mould part of thepreceding figures, relative to the radial deformation means, shown inits normal position and active position respectively.

FIGS. 5A and 5B show an enlarged detail of that mould part of thepreceding figures, relative to a modified embodiment of the radialdeformation means, shown in its normal position and active positionrespectively.

FIG. 6A is a front view of the embodiment shown in FIG. 5A.

FIG. 6B shows a portion of a section taken on the transverse planeVIB-VIB of FIG. 5B, relative to a different embodiment of the secondtube piece 24.

FIG. 7 is an axial section through that mould part incorporating asecond embodiment of the invention.

FIGS. 7A, 7B and 7C show that mould part of FIG. 7 in three successiveworking stages.

FIGS. 8A and 8B show an enlarged detail of that mould part of FIGS. 6and 7, relative to the radial deformation means, shown in its normalposition and active position respectively.

FIG. 9 is a front view of FIG. 8A.

FIG. 10 is an enlarged detail, similar to FIG. 2, of a third embodimentof the invention.

FIGS. 11A and 11B show an enlarged detail of that mould part of FIG. 10,relative to the radial deformation means, shown in its normal positionand active position respectively.

FIG. 12 is an enlarged detail, similar to FIG. 2, of a fourth embodimentof the invention.

FIG. 13 is the section on the plane XIII-XIII of FIG. 12.

FIGS. 14A and 14B show an enlarged detail of that mould part of FIG. 12,relative to the radial deformation means, shown in its normal positionand active position respectively.

The plastic container 50 to be produced comprises a tubular body 51 anda headpiece 52 which is bonded to one end of the tubular body 51; thetubular body is formed in a previous stage, whereas the headpiece 52 isformed and simultaneously bonded to the tubular body 51 within thepresent mould; finally, the other end of the tubular 25 body 51 isclosed in a subsequent stage.

Usually, the headpiece 52 possesses a tubular threaded mouth, throughwhich the contents are extracted.

The mould comprises a punch 10 having an outer tube piece 11 and acoaxial inner body within the tube piece 11. The outer surface 11′ ofthe outer tube piece 11 is cylindrical and is arranged to engage as anexact fit the tubular body 51 of the container, which is drawn over thepunch 2 during its axial penetration by this latter.

The inner body 12 comprises an end portion 13 which projects axiallydownwards from the lower end of the outer tube piece 11 and has a lowerconvex surface 13′ which converges overall downwards towards the axis.

In the embodiment shown in the figures, the punch 10 possesses a lowerlyclosed inner axial cavity in which an inner coaxial tube 15 ispositioned to define an inner chamber 16′ and an annular outer chamber16″; means (of known type, not shown in the figures) are located in theinner chamber 16′, for cooling the punch.

On the lateral surface of the punch 10 at a predetermined distance fromthe lower end of the punch, there is positioned, projecting radiallyoutwards, a ring 17 which serves as an abutment element for the upperend of the tubular body 51, to determine the axial position thereof.

Below and coaxial to the punch 10 there is provided a die 30 (of knowntype and illustrated only schematically in the figures) having a concavesurface 31′ which, in combination with the lower surface 13′ of the endportion 13 of the punch, defines a cavity F for forming the headpiece 52of the container and for pressure-bonding it to the lower end of thetubular body 51.

Specifically, said surfaces 13′ and 31′ are suitably shaped to define atubular threaded mouth 52′ on the body 52; for this purpose the lowerend 14 of the portion 13 is closed and is contacted by an axialcylindrical core 33 sealedly slidable axially through an axial hole 34provided in the die 30, with suitable means (not shown in the figures)upwardly urging the core 33 which normally projects upwards from thehole 34 to a considerable extent and is moved downwards followingcontact by the end portion 13 when the punch 10 engages the die 30.

With the concave surface 31′ of the die 30 there is associated acylindrical concave surface 32′, which lies above it as a continuationof its upper edge, to receive as an exact fit, by axial penetration, thelower end of the cylindrical outer surface 11′ of the punch togetherwith the lower end of the tubular body 51 of the container. There isalso provided a frusto-conical surface 35′ lying above and adjacent tothe surface 32′, to act as a lead-in for the penetration of the punch10.

According to the invention, the punch comprises a radial deformation(expansion) means positioned on its cylindrical outer surface 11′ andextending annularly along the entire circumference of this surface 11′,to act against the inner surface of the tubular body 51 of the containerin correspondence with the cylindrical concave surface 32′ of the die30.

In the first embodiment, shown in FIGS. 1, 2, 4A and 4B, the radialdeformation means is positioned in an annular chamber 21 formed in theouter tube piece 11 of the punch and opening into the cylindrical outersurface 11′.

For practical and constructional reasons the outer tube piece 11 of thepunch is axially divided into three segments side-by-side in thelongitudinal direction, the annular chamber 21 being formed partly inthe lower segment 111 and partly in the intermediate segment 112. Theradial deformation means comprises a flexible annular element 22,consisting of a sleeve of elastomeric material, the axial sectionthrough which is relatively narrow and elongate in the longitudinaldirection, it being positioned to close the open side of the annularchamber 21. The sleeve 22, the outer surface of which does not normallyproject outwards from the annular chamber 21 (see FIG. 4A), is radiallylocked by two annular edges 211, one upper and the other lower, whichproject in an axial direction towards the interior of the annularchamber 21.

By means of conduits 231 provided within the intermediate segment of thetube piece 11, and internal second conduit 232, the annular chamber 21communicates with means (of known type, not shown in the figures) forfeeding pressurized fluid (in particular air), the sleeve 22 beingarranged to flex within the axial plane following the feed ofpressurized fluid into the chamber 21.

Consequently, the sleeve 22 assumes a normal position in which its outersurface, the chamber 21 not being pressurized, does not project radiallyfrom the cylindrical outer surface 11′ of the punch (see FIG. 4), and anactive position in which, pressurized fluid having been fed into thechamber 21, it is pressed in the centrifugal direction to press againstthe tubular body 51 and this against the cylindrical concave surface 32′of the die (see FIG. 4B), this being the state during the forming of thecontainer headpiece 52.

Preferably the cross-section through said flexible annular element 22comprises an intermediate portion of greater diameter, projectingtowards the opposing surface of the die (see FIGS. 5A and 5B).

During the forming operation the annular chamber 21 is initiallynon-pressurized, the radial deformation means hence being maintained inits normal position.

Initially, the tubular body 51 of the container is separate from thepunch 10 and is drawn over the cylindrical surface 11′ of the punch bythe axial movement of the container tubular body 51 (see FIG. 3A),whereas the punch 10 remains at rest for the entire forming operation,As the radial deformation means is in its normal position (see FIG. 4A),the sleeve 22 does not create an obstacle to the penetration of thepunch.

A ring of elastomeric material 52, the mass of which defines apredetermined blank for producing the container headpiece 52, is theninserted into the cavity of the die 30, and immediately afterwards thedie 30 is moved upwards (see FIG. 3B).

In the next stage (see FIG. 3C), the lower end of the punch 10, togetherwith the lower end of the container tubular body 51, penetrates into thecavity of the die 30, the radial deformation means being always in itsnormal position and hence not creating an obstacle to the axialpenetration of the lower end of the cylindrical outer surface 11′ of thepunch (together with the lower end of the tubular body 51) within thecylindrical concave surface 32′. As soon as this penetration iscomplete, compressed air is fed into the chamber 21 so that the sleeve22 flexes and is urged in the centrifugal direction to press the tubularbody 51 against the cylindrical concave surface 32′ of the die (see FIG.4B).

During this stage (also shown in FIGS. 1 and 2), as a result of themutual approach of the die and punch, the ring 55 is also compressedand, being in a pasty state, completely fills the forming chamber F toform the container headpiece 52 which simultaneously becomes bonded bythermoforming to the lower end of the tubular body 52 of the container;at the same time, the sleeve 22 creates, between the punch cylindricalsurface 11′ and the cylindrical concave surface 32′, an annular barrierwhich hermetically and effectively seals the forming chamber F, toprevent seepage of plastic material and hence prevent the formation ofundesired filament-like protuberances within the container 50.

In the next stage the die 30 is moved downwards away from the punch 10and the container 50 is withdrawn from the punch (see FIG. 3D).

In the embodiment shown in FIGS. 4A and 4B the sleeve 22 acts bydirectly contacting the tubular body 51, whereas in the modifiedembodiment show in FIGS. 5A and 5B there is associated with saidelastomeric sleeve 22 an outer annular metal band 24, elasticallyexpandable in a radial direction, which is positioned on the outside ofthe sleeve 22 to act by contacting the tubular body 51. The annular band24 serves to normally contain the sleeve 22 within the chamber 21 (seeFIG. 5A). On feeding compressed air into the chamber 21, the sleeve 22flexes and is urged in the centrifugal direction in such a manner as toradially expand the band 24 and cause it to press the tubular body 51against the cylindrical concave surface 32′ of the die (see FIG. 5B); inthis case the edges 211 are not provided, and the chamber 21 iscompletely open towards the opposing die.

In the version shown in FIG. 6A, the outer annular band 24 isinterrupted by an oblique T cut, with its ends 241 lying close to eachother.

In the version shown in FIG. 6B, the outer annular band 24 isinterrupted, with its ends 242 superposed and in mutual contact.

In the second embodiment, shown in FIGS. 6-9, the radial deformation(expansion) means operates following the mutual axial approach of theentering punch 10 and the cavity of the die 30. Said deformation meanscomprises, expandable in the radial direction, a substantially flat andnormally undulated annular element 25 of elastically flexible material(for example steel), the axial section through which extends in a radialdirection, and a radial annular chamber 26, provided within the punch 10and opening into the cylindrical outer surface 11′ thereof, it being ofvariable axial dimension.

In the embodiment shown in FIGS. 8A and 9, the expandable element 25presents undulations along its cylindrical sections; alternatively theundulations can extend along its axial section.

In this embodiment the punch 10 comprises two parts movable relative toeach other in an axial direction: a first part defined by an inner tubepiece 12 a, and a second part defined by an outer tube piece 11 a whichpresents said cylindrical outer surface 11′. Said two parts 11 a and 12a are movable relative to each other in an axial direction.

The inner tube piece 12 a is integral with the end portion 13, whichprojects axially downwards from the lower end of the outer tube piece 11a, and of which the lower surface 13′ defines, together with the concavesurface 31′ of the die 30, the forming cavity F.

The outer tube piece 11 a possesses at its lower end a downwardly facingradial annular surface 41, whereas the inner tube piece 12 a possessesan upwardly facing radial annular surface 42 faced a short distancetherefrom by the other radial surface 41, the surfaces 41 and 42defining the upper and respectively lower surface of the radial annularchamber 25 (see FIGS. 8A, 8B and 9 in particular).

The inner tube piece 12 a possesses at its upper end a larger-diameterportion defining a downwardly facing shoulder 44 which comes intocontact with a corresponding shoulder 43 provided on the inner surfaceof the outer tube piece 11 a. The contact between the two shoulders 43and 44 prevents the inner tube piece 12 a from withdrawing downwardsfrom the outer tube piece 11 a; the said shoulders are in such mutualgeometrical relationship that when they are in contact, the axialdimension (which is a maximum) of the annular chamber 26 is such as tocontain the annular element 22 when in its normal configuration, i.e.released (see FIG. 8A).

The chamber 26 is arranged to contain the annular element 25 such thatits outer peripheral edge normally does not project outwards from thechamber, and is able to decrease its axial dimension during the formingof the headpiece 52, following the axial approach of the punch 10towards the cavity of the die 30, to such an extent as to causecompression of the annular element 25 and consequently its centrifugalexpansion in such a manner as to press the tubular body 51 of thecontainer against the cylindrical concave surface 32′ of the die (seeFIG. 8B).

The outer tube piece 11 a is fixed, and in particular is rigid with afixed part of the structure (not shown in the figures) of the machinewhich carries out the operation. In contrast, the inner tube piece 12 acan slide axially through a short distance relative to the tube piece 11a, between a normal position in which the shoulders 43 and 44 are inmutual contact and the end portion 13 projects to its maximum extentfrom the outer tube piece 11 a, and a retracted position in which theinner tube piece 12 a has re-entered the tube piece 11 a to its maximumextent and the chamber 26 reduces its axial dimension to its minimumvalue.

During the forming operation, the punch 10 and the die 30 are made toapproach each other after drawing the tubular body 51 of the containerover the outer cylindrical surface 11′ of the punch and after insertinginto the cavity of the die 30 a ring of elastomeric material 55, themass of which defines a predetermined blank for forming the headpiece 52of the container, all as already described for the first embodiment.

The shoulders 43 and 44 are initially in mutual contact, the annularchamber 21 has its maximum axial dimension, and the expandable element25 is in its released (and hence undulated) configuration.

As the die 30 rises towards the punch 10 to compress the elastomericring 55 within the chamber F (as shown by the position sequence of FIGS.7A, 7B and 7C), the axial dimension of the chamber F decreases (untilthe final dimension is achieved in which the material of the ring 55completely fills the chamber).

At the same time, the thrust of the rising die 30 causes the end portion13 to move upwards by virtue of the reaction of the material of the ring55; this causes axial compression of the annular chamber 26 and hencecompression of the expandable annular element 25, with the result thatthis expands in a centrifugal direction such as to press, with its outerperipheral edge, the container tubular body 51 against the cylindricalconcave surface 32′ of the die (see FIG. 8B).

This action is facilitated by the fact that the inner peripheral edge ofthe element 25 is in contact with the inner axial wall of the chamber 26and the element 25 can expand only in a centrifugal direction.

The element 25 therefore creates, against the cylindrical concavesurface 32′, an annular barrier which hermetically and effectively sealsthe forming chamber F, to prevent seepage of plastic material and henceprevent the formation of undesired filament-like protuberances withinthe container 50.

The third embodiment, shown in FIGS. 10, 11A and 11B, differs from thefirst embodiment in that the radial deformation means is positioned inan annular chamber 61, provided within the die 30 and open towards thecylindrical outer surface 32′ thereof. Specifically, said means acts bydirectly contacting the tubular body 51 of the container and is in theform of a sleeve 62 of elastomeric material (similar to the sleeve 22 ofthe first embodiment), its section being relatively narrow and elongatein a longitudinal direction.

This sleeve 62 is positioned to close the annular chamber 61, its outersurface not normally projecting outwards from the annular chamber 61,i.e. beyond the line of the cylindrical surface 32′; in addition, onfeeding pressurized fluid into the chamber 61 the sleeve 62 flexeswithin the axial plane until it presses the tubular body 51 against theopposing cylindrical surface 11′ of the punch 10; in this respect, theannular chamber 61 is connected to pressurized fluid feed means (notshown in the figures) via conduits 63.

Its operation is similar to that already described for the firstembodiment: the annular chamber 61 is initially not pressurized andhence the radial deformation means is maintained in its normal position;as it is in its normal position (see FIG. 11A), the sleeve 62 creates noobstacle to the penetration in an axial direction of the lower end ofthe punch 10, together with the lower end of the tubular body 51 of thecontainer, into the cavity of the die 20 via the cylindrical concavesurface 32′. As soon as this penetration has taken place, compressed airis fed into the chamber 61 so that the sleeve 62 flexes and acts in thecentrifugal direction to press the tubular body 51 against thecylindrical surface 11′ of the punch 10 (see FIG. 11B). The sleeve 22therefore creates, between the punch cylindrical surface 11′ and thecylindrical concave surface 32′, an annular barrier which hermeticallyand effectively seals the forming chamber F, to prevent seepage ofplastic material and hence prevent the formation of undesiredfilament-like protuberances within the container 50.

In the embodiment shown in FIGS. 10-11B, the flexible annular element 62acts by directly contacting the tubular body 51 of the container and islocked in the radial direction by two annular edges 61 1, one upper andthe other lower, which project in an axial direction towards theinterior of the annular chamber 21, such that its outer surface does notnormally project outwards from the annular chamber 21 (see FIG. 11A).Its cross-section comprises an intermediate portion of greater diameterwhich projects towards the opposing surface of the punch and is insertedbetween the edges 611 until flush with the cylindrical surface 31′.

In the fourth embodiment (FIGS. 12-14B), which is similar to the secondembodiment (FIGS. 6-9), the radial deformation means operates followingthe mutual axial approach of the entering punch 10 and the cavity of thedie 30. Again in this case, the radial deformation means comprises anannular element 65 deformable in the radial direction, and a radialannular chamber 66 provided within the die 30 and opening into itsconcave surface 32′, to contain said annular element 65 such that itsinner peripheral edge does not normally project outwards from theannular chamber 66, said deformation element 65 being made to contractin the radial direction as a result of the mutual axial approach of theentering punch 10 and the cavity of the die 30, such as to press thetubular body 51 against the opposing surface of the punch.

In the embodiment shown in FIGS. 12-14B, said annular chamber 66 isprovided within the die 30 and possesses a surface 66′ inclineddownwards towards the punch 10. The contractable element 65 ispreferably of very elastic steel, its circumference being interrupted bya transverse cut and its outer surface 65′ being inclined, to mate withthe inclined surface 66′ of the chamber 66.

The punch 10 also comprises abutment means 72 movable rigidly with it,to move the contractable element 65 downwards along the inclined surface66′ of the chamber 66 following mutual axial approach of the enteringpunch 10 and the cavity of the die 30, to cause radial contraction ofthe element 65 towards the opposing surface of the punch 10.

In detail, the chamber 66 opens upperly into an upwardly facing upperhorizontal surface 68 of the die 30. On the top of the ring 65 there arerested a number (six in FIG. 13) of small vertical pushers 69, angularlydistributed in a regular manner about the punch 10 and resting withtheir upper end on the top of the ring 65. The pushers 69 are insertedaxially slidable into suitable holes 71 a of vertical axis, providedwithin a ring 71 fixed to the upper surface 68 and surrounding theannular chamber 66. If released, the ring 65 projects axially outwardsfor a certain distance above the upper surface 68 (see FIG. 14A), untilit strikes a limit stop provided in the ring 71, to raise the pushers69, the upper end of which projects outwards in a upward direction fromthe holes 71A.

With the punch 10 there is rigidly associated an abutment ring 72 toabut against the pushers 69 and to push them through a certain distancedownwards.

During the forming operation, the punch 10 and the die 30 are made toapproach each other, after drawing the container tubular body 51 overthe outer cylindrical surface 11′ of the punch and after inserting intothe cavity of the die 30 a ring of elastomeric material 55, the mass ofwhich defines a predetermined blank for producing the headpiece 52 ofthe container, in a manner similar to that described for the firstembodiment.

The ring 65 is in its released configuration and hence does not projectradially beyond the line of the cylindrical surface 32′.

Consequently the ring 65 does not hinder the penetration in the axialdirection of the lower end of the punch 10, together with the lower endof the container tubular body 51, into the cavity of the die 30 via thecylindrical concave surface 32′.

As the punch 10 continues its penetration, the abutment ring 72, by wayof the pushers 69, pushes the ring 65 downwards, which by the action ofthe mutually engaged and sliding inclined surfaces 65′ and 66′,contracts its diameter by projecting in a centripetal direction to pressthe tubular body 51 against the cylindrical surface 11′ of the punch 10(see FIG. 14B). The sleeve 22 consequently creates, between thecylindrical surface 11′ of the punch 10 and the cylindrical concavesurface 32′, an annular barrier which hermetically and effectively sealsthe forming chamber F, to prevent seepage of plastic material and henceprevent the formation of undesired filament-like protuberances withinthe container 50.

Numerous modifications of a practical and applicational nature can bemade to the invention, but without leaving the scope of the inventiveidea as claimed below.

1. A mould for forming the top of deformable tubular plastic containerscomprising a tubular body (51) and a headpiece (52) of plastic materialbonded to one end of the tubular body (51 ), the mould comprising: apunch (10) having an outer surface (11′) arranged to engage thecontainer tubular body (51) as an exact fit, and an end portion (13)projecting axially from the lower end of the cylindrical outer surface 8(11′) and a die (30) arranged to form, in combination with the lowersurface (13′) of the punch, a cavity (F) for forming the headpiece (52)of the container, said die (30) having a concave surface (32′) arrangedto receive as an exact fit, by axial penetration, the lower end of thecylindrical outer surface (11′) of the punch together with the lower endof the tubular body (51) of the container, the headpiece (52) beingformed within the forming cavity (F) and being pressure-bonded thereinto the lower end of the tubular body (51), the punch (10)/die (30)comprising a radial deformation means (22, 20 25, 62, 65), positioned onits outer surface (11′)/concave surface (32′), which extends annularlyalong the entire circumference of this surface to act on the tubularbody (51) of the container, and is arranged to assume a normal positionin which its outer surface does not project radially from thecylindrical outer surface (11′) of the punch/from the concave surface(32′) of the die (30), and an active position in which it is urged in aradial direction in such a manner as to press the tubular body (51)against the opposing surface of the die/punch, characterised in thatsaid radial deformation means are positioned within an annular chamber(21, 61) which is provided in the punch (10)/die (30), is open towardsthe cylindrical outer surface (11′) of the punch/the concave innersurface (32′) of the die, and is in the form of a flexible annularelement (22, 62) positioned to close the annular chamber (21, 61) butwith its outer surface not normally projecting from the annular chamber(21, 61), said annular element (22, 62) being arranged to deformradially until it presses the tubular body (51) against the opposingsurface (32′) of the die (30)/against the opposing surface (11′) of thepunch, as the result of feeding pressurised fluid into the chamber (21,61).
 2. A mould as claimed in claim 1, characterised in that saidflexible annular element (22, 62) acts by directly contacting thetubular body (51) of the container.
 3. A mould as claimed in claim 1,characterised in that said flexible annular element (22, 62) is in theform of a sleeve of elastomeric material, the section through which isrelatively narrow and elongate in a longitudinal direction.
 4. A mouldas claimed in claim 3, characterised in that the cross section throughsaid flexible annular element (22, 62) comprises an intermediatelarger/narrower-diameter portion projecting towards the opposing surfaceof the die/punch.
 5. A mould for forming the top of deformable tubularplastic containers comprising a tubular body (51) and a headpiece (52)of plastic material bonded to one end of the tubular body (51), themould comprising: a punch (10) having an outer surface (11′) arranged toengage the container tubular body (51) as an exact fit and an endportion (13) projecting axially from tie lower end of the cylindricalouter surface 8 (11′) and a die (30) arranged to form, in combinationwith the lower surface (13′) of the punch, a cavity (F) for forming theheadpiece (52) of the container, said die (30) having a concave surface(32′) arranged to receive as an exact fit, by axial penetration, thelower of the cylindrical outer surface (11′) of the punch together withthe lower end of the tubular body (51) of the container, the headpiece(52) being formed within the forming cavity (F) and beingpressure-bonded therein to the lower end of the tubular body (51), thepunch (10)/die (30) comprising a radial deformation means (22, 20 62,65), positioned on its outer surface (11′)/concave surface (32′) whichextends annularly along the entire circumference of this surface to acton the tubular body (51) of the container, and is arranged to assume anormal position in which its outer surface does not project radiallyfrom the cylindrical outer surface (11′) of the punch/from the concavesurface (32′) of the die (30), and an active position in which it isurged in a radial direction in such a manner as to press the tubularbody (51) against the opposing surface of the die/punch, characterisedin that said radial deformation means are positioned within an annularchamber (21, 61) which is provided in the punch (10)/die (30), is opentowards the cylindrical outer surface (11′) of the punch/the concaveinner surface (32′) of the die, and is in the form of a flexible annularelement (22, 62) positioned to close the annular chamber (21, 61) butwith its outer surface not normally projecting from the annular chamber(21, 61), said annular element (22, 62) being arranged to deformradially until it presses the tubular body (51) against the opposingsurface (32′) of the die (30)/against the opposing surface (11′) of thepunch, as the result of feeding pressurised fluid into the chamber (21,61); said flexible annular element (22, 62) is in the form of a sleeveor elastomeric material, the section through which is relatively narrowand elongate in a longitudinal direction; and with said flexible annularelement (22) there is associated a second metal sleeve (24) elasticallyflexible in radial direction, and interposed between the tubular body(51) and the sleeve of elastomeric material (22).
 6. A mould as claimedin claim 1, characterised in that said radial deformation meanscomprises a normally undulated annular element (25) of elasticallyflexible material, the axial section through which extends in a radialdirection, and a radial annular chamber (26) provided within the punch(10) and opening into the cylindrical outer surface (11′) thereof, itbeing of variable axial dimension and being arranged to contain saidannular element (25) in such a manner that the outer peripheral edge ofthis latter does not normally project outwards from the annular chamber(26), said annular chamber (26) being able to decrease its axialdimension during the forming of the headpiece (52) to such an extent asto cause compression of the annular element (25), with its consequentradial expansion such that it presses the tubular body (51) against thecylindrical concave surface (32) of the die.
 7. A mould as claimed inclaim 6, characterised in that the punch (10) comprises two partsmovable relative to each other in an axial direction, a first part (12a) rigid with the end portion (13) and having an upwardly facing radialsurface (42), and a second part (11 a) which presents said cylindricalouter surface (11′) and has a downwardly facing radial surface (41),said radial surfaces (41, 42) facing each other and defining the lowerand respectively upper surface of said radial annular chamber (26).
 8. Amould as claimed in claim 1, characterised in that said radialdeformation means comprises an annular element (65), contractable in aradial direction, and a radial annular chamber (66) provided within thedie (30) and opening into its concave surface (32) to contain saidannular element (65) in such a manner that the inner peripheral edge ofthis latter does not normally project outwards from the annular chamber(66), said contractable element (65) being made to contract in a radialdirection as a result of the mutual axial approach of the entering punch(10) and the cavity of the die (30), in such a manner as to press thetubular body (51) against the opposing surface of the punch.
 9. A mouldas claimed in claim 8, characterised in that: said annular chamber (66)is provided within the die (30) and possesses a surface (66′) inclineddownwards towards the punch (10), said deformable element (65) possessesan inclined outer surface (65′) which mates with the inclined surface ofthe chamber (66), and the punch comprises abutment means (72) movablerigidly with it, to move the deformable element (65) downwards along theinclined surface (66′) of the chamber (66) following mutual axialapproach of the entering punch (10) and the cavity of the die (30), tocause radial contraction of the element (65) towards the opposingsurface of the punch (10).